Conventional cardiac surgery provides excellent access and visualization for correction of structural heart defects; however, it requires opening the chest and operating on an arrested, non-beating heart. Although endoscopic surgery has been successfully used in abdominal and thoracic surgery, difficulties in obtaining a clear and wide field of vision in blood have prevented its use in cardiac surgery. We have developed a novel approach for clear visualization of intracardiac anatomy in the beating heart using a flexible fiberoptic cardioscope and two extracorporeal bypass circuits. The primary cardiopulmonary bypass circuit secures hemodynamic stability by providing systemic and coronary perfusion. The second imaging circuit is used to isolate the heart from the systemic circulation by perfusing a clear fluid through the heart chambers for intracardiac visualization. Preservation of normal heart movement and clear visualization of intracardiac structures should allow for safer and more effective surgical interventions while avoiding the risk of myocardial injury that can occur in an arrested heart. Iterative surgical interventions can be performed within a beating heart guided by functional intracardiac evaluation without the risk of sudden hemodynamic compromise. In valve repair/replacement and annuloplasty procedures, the clinician can evaluate valve function and morphology during annular contractions before and after intervention. The goal of this proposal is to establish clinically applicable, less invasive nd percutaneous approaches to intracardiac surgery under direct visualization in the beating heart. To achieve our goal, we have three specific aims. Specific Aim 1 is to develop and test a simplified imaging bypass circuit and cannulae to visualize intracardiac structures on the left side of the heart using less invasive surgical and percutaneous approaches to the LV. The imaging bypass circuit will be between the pulmonary artery (PA) (outlet) and the left ventricle (LV) (return). A PA balloon cannula placed from a peripheral vein will be used to occlude the PA, isolate the LV from the right ventricle and flush blood out of the pulmonary circulation into the LV using a clear imaging fluid. The imaging fluid return cannula and the cardioscope will be placed into the LV. Specific Aim 2 and 3 are to validate that both a less invasive and percutaneous visualization system will allow for the safe and effective performance of intracardiac surgeries on a beating heart in an animal model. These include mitral valve repair and the resection of parts of the LV septal wall. The Cardioscope will be placed near the LV apex via a small thoracotomy or small subxiphoid incision or across the aortic valve via the carotid or femoral artery percutaneous approach. The successful completion of this research will provide clinicians with a versatile less invasive platform for closed-chest, intracardiac surgery o electrophysiological interventions in a beating heart. This technique could replace many invasive surgical procedures that require a sternotomy, eliminate added risks from re-operations and provide a safer approach for high risk and elderly patients with valve regurgitation.